A University of Utah team has built a lightweight robotic hip exoskeleton that helps stroke survivors walk with less effort. Early results show it can significantly reduce the energy cost of every step.
For millions of stroke survivors, simply walking across a room can feel like climbing a hill with a heavy pack on their back. A new robotic hip exoskeleton from University of Utah engineers aims to lighten that load.
In a pilot study published in the journal Nature Communications, researchers from the John and Marcia Price College of Engineering and the College of Health showed that a portable, 5.5-pound hip exoskeleton can cut the energy needed to walk by nearly 20% for people living with hemiparesis, a common aftereffect of stroke that weakens and stiffens one side of the body.
The device, worn around the hips and strapped to the thighs, uses battery-powered motors to help move each leg with every step. An onboard control system senses the user’s motion in real time and delivers a boost when the hip needs to lift the leg or push off, making each step more efficient.
Hemiparesis affects about 80% of stroke survivors and is a leading cause of disability in the United States. Because one side of the body is weaker, the other side has to work harder to compensate. That imbalance can make walking 60% more energy-intensive than it is for people with a typical gait, leading to slower speeds, fatigue, pain and a higher risk of falls.
“Improving quality of life after a stroke is one of the biggest unmet challenges in healthcare today,” senior author Tommaso Lenzi, an associate professor in the Department of Mechanical Engineering, said in a news release. “We’re now showing that robotics can make a measurable impact here.”
The Utah team’s approach stands out from earlier efforts that focused on the ankle. Many researchers have tried to solve post-stroke walking problems with powered ankle braces, because issues like foot drop and weak push-off at the ankle are easy to see. But those devices have not delivered the hoped-for gains.
“Portable ankle exoskeletons have failed to reduce the energy required for stroke patients to walk, so we proposed a different approach,” added lead author Kai Pruyn, a graduate student in Lenzi’s HGN Lab for Bionic Engineering.
Pruyn and colleagues realized that when the ankle is weak, people often compensate by working their hip muscles much harder, which burns extra energy. That insight led them to design a hip-focused device instead.
“Patients with ankle weakness often compensate with their hip joints, which requires extra energy. Our goal was to develop a powerful and fully portable hip exoskeleton,” Pruyn added. “Hip exoskeletons can also be extremely lightweight because they are worn closer to the user’s center of mass and have lower torque requirements compared to ankle exoskeletons. We found that the hip assistance effectively compensated for reduced ankle propulsion.”
Lenzi’s lab is known for wearable robotics, including the Utah Bionic Leg, which was named one of Time magazine’s top inventions in 2023. Other groups have tested hip exoskeletons in healthy volunteers and shown they can improve walking efficiency. The Utah study is the first to demonstrate clear benefits for people with hemiparesis after stroke.
To test the new device, the researchers brought seven stroke survivors with hemiparesis into the lab. Using precise motion-capture cameras and an instrumented treadmill, they recorded how each participant walked with and without the exoskeleton. The volunteers also wore equipment that estimated how many calories they burned in each condition.
From those measurements, the team calculated the metabolic cost of walking. With the exoskeleton turned on, the device took over nearly 30% of the work normally done by the hip joints. That assistance translated into an 18% drop in the overall energy cost of walking.
Co-author Bo Foreman, a professor of physical therapy and athletic training, compared the difference to shedding a heavy load.
“For a person with a healthy gait, this would be like taking off a 30-pound backpack,” he said in the news release. “For someone with hemiparesis, that’s a life-changing difference.”
Study participants felt the change in their everyday movements. One stroke survivor, Lidia, described how limited she was before trying the device. “In the beginning, I couldn’t move my leg,” she said. “But with the device, it’s much better now.”
“In the beginning, I couldn’t move my leg,” said stroke survivor Lidia, one of the participants. “But with the device, it’s much better now.”
Her husband, Marcellus, noticed that the benefits carried over even when she was not wearing the exoskeleton.
“In a way, the exoskeleton was doing some of that movement for her,” he said. “The more we used it, the better she was when she wasn’t using it.”
That kind of carryover hints at a powerful possibility: by making walking easier and more symmetrical, the exoskeleton might not only assist movement in the moment but also help retrain the nervous system over time. While the current study focused on immediate energy savings, future research could explore whether regular use leads to lasting improvements in strength, coordination and confidence.
The device itself is designed with daily life in mind. At just 5.5 pounds and worn close to the body’s center of mass, it is far lighter and less bulky than many earlier exoskeletons. The motors and control system are fully portable, so users are not tethered to a power source or lab equipment.
Still, there is work to do before such a system could be prescribed like a brace or walker. The next steps for Lenzi’s team include testing the hip exoskeleton outside the lab to ensure it is safe and effective at home and in the community. That means refining the mechanics and control software so the device can handle real-world challenges such as turning, climbing stairs, standing up from a chair and navigating uneven ground.
The lab is partnering with leaders in prosthetics and orthotics to translate the prototype into a product that clinicians could fit and adjust for individual patients. That kind of collaboration will be key to making the technology affordable, durable and easy to use.
The team’s ultimate aim goes beyond engineering.
“Our goal is to ensure that a stroke doesn’t define the limits of where a person can go or how they can live,” Lenzi added.
If the early results hold up in larger, longer-term trials, lightweight hip exoskeletons could become a new tool in stroke rehabilitation, helping survivors trade that invisible 30-pound backpack for a freer, more independent life.
Source: University of Utah